1. Field of the Invention
The present invention relates to a two-color molding method of thermoplastic resin by injection molding, more particularly relates to a two-color molding method for molding a shaped article comprised of a main part and packing part which molds the main part by a second thermoplastic resin and molds the packing part by a first thermoplastic resin.
2. Description of the Related Art
When it is necessary due to the demands for physical properties or design to mold one article from a plurality of types of resins or a plurality of the same type of resin having different colors, the two-color molding method has been employed in the past. This two-color molding method first injects a first molten resin into a first cavity to mold a first resin part, then injects a second molten resin into the second cavity adjacent to the first cavity to mold a second resin part. By doing so, the first resin part and the second resin part are melt bonded together to form an integrated two-color shaped article.
With this two-color molding method, it is necessary to partition the first cavity and the second cavity so as to limit the flow of the first molten resin to the second cavity. As this method, when using a plurality of different molds, there is the method of partitioning the molds themselves, but when using one type of mold, as described in Japanese Patent Publication (A) No. 11-48284, partitioning by a slide core (movable partitioning member) is often used.
On the other hand, one cycle of the shaped article production time for molding one or one set of two-color shaped articles is basically comprised of a step of closing the mold, a step of injecting a molten resin into the mold cavity, a step of cooling and solidifying the molten resin, a step of opening the mold, and a step of taking out the shaped article from the mold. However, when repeating the method of molding described in Japanese Patent Publication (A) No. 11-48284 to produce two-color shaped articles in large quantities, one cycle of the shaped article production time (hereinafter referred to as the “cycle time”) becomes longer. This is mainly because when the mold is closed, the first resin and second resin are injected for molding, so the time when the mold is opened does not contribute at all to the molding of the resin.